Fossils uncovered in San Diego 25 years ago show that humans inhabited North America at least 115,000 years earlier than previously thought, according to researchers. NBC 7's Llarisa Abreu reports. (Published Wednesday, April 26, 2017)

Fossils uncovered in San Diego 25 years ago show that humans inhabited North America at least 115,000 years earlier than previously thought, according to researchers.

The San Diego Natural History Museum announced the findings to the public on Wednesday.

Sites with evidence of humans in North America are typically around 14,000 years old. Some researchers now believe the San Diego site marks a much older beginning of humans in North America, though that is not definitive.

The site included clusters of rocks believed to have been used as tools. Richard Fullagar of the University of Wollongong, Australia, confirmed stones found at the San Diego site showed the same wear marks as stones used as tools in other sites.

But some are skeptical that the rocks were really used as tools. Vance Holliday of the University of Arizona in Tucson told The Associated Press the paper shows the bones could have been broken the way the authors assert, but they haven't demonstrated that's the only way.

Richard Cerutti's discovery of mysterious mastodon bones in San Diego launched a 22-year investigation which lead to the conclusion that humans roamed our backyards over 130,000 years ago.
Photo credit: NBC 7

Steve Holen, former curator of archaeology at the Denver Museum of Nature & Science, traveled to San Diego in 2008. His experiments about stone tools were used to determine some of the bone fragments were broken apart in that way.

Holen called the discovery the biggest shock of his scientific career.

“Once I realized in my mind how old this site was, I could not believe that humans were here at that time,” Holen said. “It went against everything I’d ever been taught and everything that I ever thought I knew. It was quite shocking.”

He said they believe the location was a place where humans took bones and made tools.

"It is one thing to show that broken bones and modified rocks could have been produced by people, which Holen and his colleagues have done," Grayson wrote. "It is quite another to show that people, and people alone, could have produced those modifications."

Richard Potts of the Smithsonian Institution's National Museum of Natural History, told The Associated Press he doesn't reject the paper's claims outright, but he finds the evidence "not yet solid."

There are plans to begin field surveys looking for other sites of a similar age in geological deposits across Southern California, Holen said. Researchers will also look at museum collections to use similar analysis on those fossils.